When causing a leg type moving robot, such as a bipedal moving robot, to perform an operation of, for example, moving a certain object by pushing, the robot is subjected not only to a floor reaction force from a floor with which a distal portion of a leg thereof is in contact but also to a reaction force from the object. The reaction force received by the robot from the object is referred to as an object reaction force in the present description.
As a technology for generating a gait of a robot or controlling an operation thereof in a state wherein an object reaction force is acting on a leg type moving robot, there has been known a technology disclosed in, for example, Japanese Patent Laid-Open No. H10-230485 by the inventor of the present application (hereinafter referred to as Patent Document 1). According to the technology, a desired gait is generated such that a dynamic balance condition in which a component (horizontal component), excluding a vertical component, of a moment produced about a desired ZMP (a desired floor reaction force central point) by a resultant force of an inertial force produced due to a motion of a robot and the gravity and an object reaction force acting on the robot is zero (a floor reaction force acting on the desired floor reaction force central point and the aforesaid resultant force are balanced with each other) is satisfied. Furthermore, according to the technology, even if an external force acting on the robot turns into an unexpected external force (even if a difference between a desired external force and an actual external force increases to a certain extent), a desired gait of the robot is adjusted such that a position of the center-of-gravity of the robot is balanced to a position of the center-of-gravity that makes it possible to maintain the dynamic balance of the robot.
Meanwhile, in order to cause a robot to perform the operation of moving an object as described above (more specifically, in order to determine a gait of the robot for carrying out the operation and to actuate the robot to follow the gait), it is necessary to determine beforehand a desired value of a force to be applied to the object from the robot or a desired value of the object reaction force. An object reaction force is obtained by reversing the sign of a force which is applied to the object from the robot, so that a desired value of an object reaction force will be representatively determined hereinafter in the explanation of the description.
In this case, the desired value of the object reaction force (hereinafter referred to as “the desired object reaction force”) will be determined on the basis of a moving plan of an object (a schedule showing the timings and methods for moving an object) or environmental conditions (e.g., the coefficient of friction between an object and a floor, and the inclination angle of the floor) predicted in advance. Furthermore, in this case, it is also possible to determine the desired object reaction force by applying a motion of the object based on the moving plan of the object to a dynamic model of the object constructed on the basis of the predicted environmental conditions (a model showing a relationship between a motion, including a velocity and a position, of the object and a force acting on the object).
However, actual environmental conditions frequently disagree with predicted environmental conditions. In such a case, there will be a discrepancy between a desired object reaction force and a real object reaction force (actual object reaction force). As a result, even when the operation of the robot is controlled so as to satisfy the dynamic balance condition of the robot on the basis of the desired object reaction force, the discrepancy between the desired object reaction force and the actual object reaction force prevents the dynamic balance condition of the actual robot from being satisfied, thus impairing the stability of the robot.
Hence, according to the aforesaid technology disclosed in Patent Document 1, the position of the center-of-gravity of a robot or the desired value of a floor reaction force is corrected to cancel the difference between a desired object reaction force and an actual object reaction force.
However, in a situation wherein a discrepancy takes place between a desired object reaction force and an actual object reaction force, another discrepancy generally takes place between a moving position of an object based on a moving plan (i.e., a desired moving position of an object) and an actual moving position of the object. In this case, the desired object reaction force will not match the actual moving position of the object. For this reason, as with the aforesaid one in Patent Document 1, even if the position of the center-of-gravity of the robot or the desired value of the floor reaction force is corrected so as to cancel the difference between the desired object reaction force and the actual object reaction force, the discrepancy between the desired object reaction force and the actual object reaction force excessively increases or the discrepancy frequently occurs in some cases. In such a case, there has been a danger in that an excessive behavior change of the robot takes place, thus making it difficult to cause the robot to successively perform the operation of moving the object while continuously maintaining the stability of the robot.
The desired object reaction force could be corrected on the basis of a detected value of the actual object reaction force. However, if, for example, the actual object reaction force suddenly changes and if the desired object reaction force is suddenly changed in response thereto, then the robot develops an excessive behavior change, which could easily impair the stability of the robot. In this case, the desired object reaction force could be slowly changed in response to the change in the actual object reaction force; however, doing so would cause a delay in the change of the desired object reaction force in response to the change of the actual object reaction force. This would prevent the dynamic stability of the robot from being promptly secured, resulting in impaired stability of the robot.
The present invention has been made with a view of the aforesaid background, and it is an object thereof to provide a controller of a leg type moving robot which uses a dynamic model of an object and which is capable of determining a desired motion of the object and a desired value of an action force between the object and the robot by using the dynamic model while minimizing a discrepancy between a motion state of the object on the dynamic model and a motion state of the actual object, thus making it possible to cause the robot to perform an operation of moving the object while securing the stability of the robot.